Catalytic reforming is a process in which hydrocarbon molecules are rearranged, or reformed in the presence of catalyst. The molecular rearrangement results in an increase in the octane rating of the feedstock. Thus, during reforming low octane hydrocarbons in the gasoline boiling range are converted into high octane components by dehydrogenation of naphthenes and isomerization, dehydrocyclization and hydrocracking of paraffins.
Naphtha reforming may also be used for the production of benzene, toluene, ethylbenzene and xylene aromatics. Generally, the molecular rearrangement of molecular components of a feed, which occurs during reforming, results in only slight changes in the boiling point of the reformate (the product of reforming).
Reformate comprises a large percentage of finished pool gasoline, up to 80% in topping-reforming refineries. With the advent of non-lead gasolines, more straight run stocks usually blended into gasoline are now reformed. Commercial reformers use a platinum containing catalyst with a hydrogen recycle stream. The typical processes can be classified initially according to the approach to catalyst regeneration, i.e., semi-regenerative, cyclic or continuous with cyclic and continuous units operated at low pressure (&lt;300 psig).
In the late 1960's platinum-rhenium bimetallic catalysts were introduced with a high selectivity for cracking. Recently, platinum and non-acidic zeolite containing catalyst compositions have been introduced in reforming. Zeolites include naturally occurring and synthetic zeolites. It has been reported that such non-acidic catalysts demonstrate superior selectivities in reforming.
More recent governmental regulations prescribing the production of cleaner fuels particularly containing less benzene, aromatics and more oxygenated compounds have technically challenged the petroleum refining industry to meet those regulations while minimizing economic upset to refinery operations and unit processes. Naphtha catalytic reforming which plays a major role in the refinery in upgrading low octane value hydrocarbons is a focal point for process improvement. Higher linear and low branched paraffin conversion to aromatics, particularly C.sub.7 + aromatics, and higher overall selectivity to high octane value compounds is sought for. It is also desirable to achieve these objectives while reducing or at least not increasing the make of low value light C.sub.1 -C.sub.4 paraffins which are typically a by-product of naphtha cracking/reforming.
The instant invention provides a major accomplishment in paraffins upgrading by dehydrocyclization/aromatization combined with cracking operations. The following patents while related to the instant invention do not teach or suggest that invention and are incorporated herein by reference in their entirety.
U.S. Pat. No. 4,867,864 to Dessau (Sep. 19, 1989) discloses a catalytic process for the conversion of a paraffin feed to effluents with increased aromaticity wherein the catalyst comprises low acid value zeolite Beta in combination with a strong dehydrogenation/hydrogenation metal.
U.S. Pat. No. 4,935,566 to Dessau, et al (Jun. 19, 1990) discloses a dehydrocyclization and reforming process for paraffins employing preferably a non acidic platinum-tin containing crystalline micro porous material.
U.S. Pat. Nos. 4,969,987 and 5,100,533 to Le et al, incorporated herein by reference, disclose a process for upgrading paraffinic naphtha by cracking over medium pore zeolite catalyst to produce at least 10 wt % isoalkene. The preferred feedstock is straight run naphtha containing C.sub.7 + alkanes, at least 15 wt % C.sub.7 + naphthenes and less than 20% aromatics.
U.S. Pat. No. 5,013,423, to Chen, et al (May 12, 1991) teaches a process for the manufacture of aromatics from normal hexane and normal heptane using a non-acidic indium catalyst containing platinum.
U.S. Pat. No. 4,035,285 to Owen (Jul. 12, 1977) discloses a process for the catalytic cracking of high boiling hydrocarbons in the presence of crystalline zeolite conversion catalyst and hydrogen.
U.S. Pat. No. 5,037,531 to Budens, et al (Aug. 6, 1991) discloses a catalytic cracking process using Y zeolite.
It is an object of the present invention to provide a process for the conversion of naphtha to high octane value hydrocarbons with a high selective conversion of acyclic paraffins, particularly low octane linear paraffins, to aromatics.
It is another object of the present invention to provide a process for the conversion of naphtha wherein a significant portion of naphthenes in the naphtha feedstream are concomitantly converted to light olefins.
Another object of the invention is to produce petrochemical feed stocks including light aromatics and light olefins from naphtha.
Yet a further object of the present invention is to provide a process for naphtha upgrading to aromatics and olefins with a reduced production of light C.sub.1 -C.sub.3 paraffins.
An additional object of the invention is to provide a process which upgrades naphtha to aromatics and branched paraffins rich gasoline and ethene, propene and butene rich light gas.